This invention relates generally to the field of orthopaedics, and to knee-replacement surgical procedures, in particular.
In total knee replacement (TKR) surgical procedures, the distal femur and proximal tibia are replaced with prosthetic elements. In conjunction with such procedures, it is also standard practice to replace the posterior portion of the patella. Making reference to FIG. 1, the quadriceps and patellar tendons, 104 and 106, respectively, are twisted to expose the posterior surface of the patella 102, and an oscillating saw is typically employed to resect the bone along a coronal plane more or less flush with the attachments of the tendons 104 and 106. Following this resection, one or more holes are ordinarily drilled into the resected surface to mate with a prosthesis, typically constructed of polyethylene, having posts which mate with the drilled holes. A central hole 108 may be formed, or a plurality of holes such as triangularly spaced-apart holes 110 may be employed, depending upon the fixation arrangement adopted by a given manufacturer.
Making reference to FIG. 2, having performed the appropriate surface preparation, the prosthetic element 202 is affixed to the patella 102 using a suitable adhesive such as polymethylmethacrylate (PMMA). The natural and artificial components are placed into a compressive tool 204 and urged together until the adhesive sets.
Unless the bone of the patella is defective, the technique just described works well for primary arthroplasty in a majority of cases. There are situations, however, wherein the attachment of a prosthetic element to the patella is somewhat more challenging. For example, if the bone is soft or otherwise compromised, the holes bored into the resected surface may not be as stable compared to situations involving healthy, harder bone stock. Problems of this type more commonly arise if, and when, the prosthesis requires revision, which may be performed in conjunction with a revision TKA, independently or if the patellar component itself, becomes loosened or damaged.
Although there are a wide variety of protocols associated with primary patella replacement, the procedures are far less developed when it comes to revision arthroplasty and procedures involving softer bone. Non-primary techniques rely more heavily on the experience of a given surgeon, and less on regimented procedures applicable to a wide variety of situations. Typically, using a revision as an example, the remaining cement must be chipped away and the previously resected surface somehow filed down to create a new host. Either the same holes used in the previous procedure are redrilled, or new ones are formed, but in any case, the result may be less than adequate, resulting in a looser fit of the prosthetic component when installed. According, any methods or apparatus which would improve procedures associated with these more challenging patella replacement surgeries would be welcomed and embraced by the orthopaedic community.
The subject invention resides in apparatus and methods for preparing the posterior surface of a patella to receive a prosthetic element. Although the invention is suited to revision procedures, wherein the posterior surface has been previously rejected, the invention is likewise applicable to primary techniques, particularly if the patella surface is soft or otherwise defective.
According to a method aspect of the invention, a layer of hardening material is applied to the posterior surface of the patella. Polymethylmethacrylate (PMMA) is the preferred choice due to its widespread use as a cement in conjunction with orthopaedic techniques. A shaped die is provided according to the invention, which is urged against the hardening material to create a reconstructed surface on the posterior surface of a patella. The reconstructed surface may then be further prepared or used directly as a host for the prosthetic element. In terms of further preparing the reconstructed surface, the method of the invention may include the step of forming one or more cavities into the posterior surface of patella prior to applying the layer of material.
The shaped die preferably includes a planar surface where it contacts the hardening material. To provide a thicker build-up, however, the die surface may be recessed relative to a peripheral edge, so that the reconstructed surface is raised relative to the posterior surface of the patella. Various articles may also be embedded into the hardening material to strengthen the reconstruction or provide attachment mechanisms. As examples, a mesh may be embedded within the material prior to hardening, or one or more cables may be added to engage with tendons attached to the patella.